The relationship between fluoride and skeletal strength and fractures is poorly understood. Recent ecologic studies have suggested that exposure to fluoridated water supplies may be associated with an increased frequency of hip fractures, but such studies have considerable potential for error in assessing fluoride exposure. Few Americans consume only beverages from a single water supply for their lifetime; additionally, fluoride has only been added to water supplies in the U.S. since the late 1940s, and widespread fluoridation only became common in the 1960s. Most Americans included in these studies were only exposed to fluoride late in life. However, these studies together with recent information from therapeutic trials using sodium fluoride have raised the possibility that fluoride exposure may increase fracture risk (excluding vertebral fractures). To address this issue we propose a study of fluoride exposure and fractures in a population with long-term stable exposures to fluoride. In rural China there is very little population mobility, and correspondingly little exposure to fluoride from sources outside the home village. We propose to: l) identify 7,500 Chinese in 50-60 villages with well-defined, long-term exposures to fluoride in a range of concentrations bracketing l ppm, the 'optimal' level used in the U.S. for fluoridation of community water supplies; 2) assess (and confirm with x-rays and medical records) the adult fracture histories of these subjects, and determine the relationship between fracture prevalence at the village level and long- term fluoride exposure; 3) measure calcium intake, physical activity (primarily labor), and other factors potentially associated with both fluoride exposure and fractures.